Tach dancing at idle (revving like cams)

[mramc3]

Ok after all the weird problems with my car, I have a new one. After replacing my o2 sensor (front) the car has been running well except for the low rpms. I started the car this morning and let it sit in neutral for 15 mins. then I adjusted the BISS screw on the throttle body so that the rpms at idle would be about 600-750rpms. So that stopped the car from always dying at a stop when i would have to press the clutch all the way in. But sure enough by the time i got to work (20 mins later, highway driving about 80mph average.) the rpms would drop and I would die everytime i stopped. I look on the intake side for leaks and found none.

What can be causing the roms to drop so drastically??? Timing belt being off? Can I check anything on the internals?

 

[mramc3]

so i replaced the o2 and reset the computer. the car wasn't revving up too well in idle so I backed out the BISS screw on the TB. The car runs fine on highway driving, but then all of a sudden, everytime I come to a stop the rom needle dances between 2.5K-3k. Pulses like i have cams or something. I've been told its an intake leak, but I just fixed all the hoses the night before. What causes the pusling?

 

[JayJones]

Mine is doing that same thing. A mechanic traced it back the Thortle Postion Sensor(TPS). I don't know if you could be your problem, but you never know

 

[mramc3]

Did the mechanic say what exactly was wrong with the TPS? I can take my DMM and check the values on it later.

 

[93awdhaitian]

Ok after all the weird problems with my car, I have a new one. After replacing my o2 sensor (front) the car has been running well except for the low rpms. I started the car this morning and let it sit in neutral for 15 mins. then I adjusted the BISS screw on the throttle body so that the rpms at idle would be about 600-750rpms. So that stopped the car from always dying at a stop when i would have to press the clutch all the way in. But sure enough by the time i got to work (20 mins later, highway driving about 80mph average.) the rpms would drop and I would die everytime i stopped. I look on the intake side for leaks and found none.

What can be causing the roms to drop so drastically??? Timing belt being off? Can I check anything on the internals?

If it only does it when it is cold it is the EGR but from how you explain it i think it is a vac leak somewhere, Make a boost leak tester and test it out and listen for any hissing of any kinda.

 

[mramc3]

If it only does it when it is cold it is the EGR but from how you explain it i think it is a vac leak somewhere, Make a boost leak tester and test it out and listen for any hissing of any kinda.

it does it even when its warm. there are soo many vaccum lines its crazy. how is the vaccum leak making the engine rev so aggressively?

 

[JayJones]

He just said it was starting to go bad. He said I could try adjusting the postion of it but doesm't know how much it could help

 

[mramc3]

im just waiting on the rain to stop, I have no garage to work on it in. yup its raining in san diego!! WTF? anyways. How does the BISS screw work? I was thinking that maybe I backed it out too much and the computer is trying to regulate the intake airflow by pulling the rpms down. I am constantly checking my vaccum lines, looking for ones i wouldnt normally lookin at. I still have the revving when the car is warm. any help please?

 

[JayJones]

When i first got my car it idled funny and jumped from 600 to 900 and ran like crap. When it was cold it idled at 2000 when warming up. I backed out the biss screw and I got my idle strong at 800 but idles at 2300 when it is warming up

 

[mramc3]

ok.. heres the update. No Vaccum leaks, or intake leaks. When starting the car (cold). It idles high at 2500 rpms then slowly creeps up to over 3200rpms. then it starts to settle and move too about 1800-2100 rpms. If I press the clutch in the car will die. If I drive it around the block (all warmed up already) the rpms will go from 2200rpms-3300rpms. Going vroom drop... vroom. drop... vroom, drop. Of course theres a ticking sound too (could be the lifters).

Any help on where to look next?

 

[mramc3]

So I had a buddy come out and look at my car. There is a vaccum unit that was doing all the ticking. My friend pulled it out and cleaned up the connection, and it started to idle fine. No more dancing tach. Supposedly there was a bad connection, but I think there is an internal problem, maybe some bad components inside. I am attaching a picture. Can someone explain what this part does and what is it so that i may replace it.

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[Greg Collier]

Having a 90 it looks either like a purge control solenoid or fuel pressure control valve.

 

[mramc3]

anyone with a 2g that can confirm that?

 

[Big Al 389]

I believe thats the solinoid for the egr,trace the vac. lines and see where they go...Al